This invention relates to a method of fastening an electrical conductor lead to each end of a ferromagnetic body or core for use in a coil assembly. The aforesaid method provides for cementing the leads to the core form in a highly effective manner as compared to prior art methods while providing the resultant structure with molded flanges on its ends to protect a coil winding disposed about the outer surface of the core form between such flanges.
Furthermore, the present invention is particularly adapted for use in the manufacture of miniature coil assemblies wherein necessarily small diameter wire leads are employed in combination with ultra-fine coil wire having a diameter on the order of one to two mils in diameter.
One of the critical problems encountered in the manufacture of miniature coils as considered hereinabove is the occurrence of loose connections between the ends of the wire leads and the ferromagnetic core body associated therewith. Should the lead ends be subject, for example, to relative rotation with respect to the core body, it becomes a distinct possibility that the connection between the fine coil wire and the leads may become broken rendering the coil assembly inoperable. Necessarily, the potential breaking of the connection between the leads and the coil winding is also a possibility should the mechanical connection between the lead and the core body be loose or defective in an axial sense. A further problem encountered in the prior art relates to protecting a fine coil winding from solder and flux splash and general process handling, for example.
The prior art has considered various methods for cementing the ends of wire leads into the opposite ends of a ferromagnetic core. Such methods have involved the provision of a closed end cavity in each end of the core in which a liquid adhesive is employed to make a bond between the lead end and the body. Usually, an upset shoulder is provided inwardly from the extreme end of the lead to abut up against the axial end face of the core form when the former is inserted into the latter. After dipping a lead end into the aforesaid liquid adhesive and inserting the same into a cavity in the end face of the core, the assembly is placed usually on a tray with other similar assemblies for transfer to an oven for curing. The mechanical fit between the inside diameter of the core cavity or aperture and the outside diameter of the lead is critical so as to maintain concentricity between the wire lead and the core. Since this method of assembly is normally performed as a manual operation it results in variations in the amount of adhesive provided for bonding whereby weak bonds have been encountered while excessive amounts of adhesive have cause lead contamination outside of the bonding area.
Furthermore, it has been recognized in the prior art that it is advantageous to provide a flange at each end of the core body which extends outwardly in a radial direction with respect thereto. Such flanges act as heat shields to protect fine coil windings disposed therebetween from solder flux splash, provide resistance to springing of coil windings and provide, in general, mechanical protection during handling of the device. In addition, such flanges provide mechanical centering for coils requiring an additional sleeve for electromagnetic shielding. The prior art has provided such flanges as an integral part of the magnetic core body, which necessarily results in a more complex core body.